What type of animal does Gregor Samsa continue to worry about, indicating that he still has lingering feelings of being another creature's prey?

Gregor Samsa continually worries about his ability to fight off the predatory advances of birds, such as when he looks at his soft skin in dismay and wonders how he will ever protect himself from birds. He also thinks about birds when deciding to get up out of bed at the start of the story. He is worried about his prone position lying on his back in bed, saying that the position allows "him no chance of surviving an attack--by predatory birds, for example" (187).